#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <map>
#include <set>
#include <unordered_map>
#include <unordered_set>
#include <climits>
#include <iomanip>
#include <cmath>
#include <string>
#include <vector>
#define int long long
#define x first 
#define y second 
using namespace std;
const int N = 1e5 + 10;
int a[N];
void solve()
{
    double n,m;
    cin >> n >> m;
    double p = m / 100;
    //cout << p << endl;
    double ans = n * (n + 1) / 2;
    double res = n / ans;
    if(res < p)
    {
        cout << "-1" << endl;
        return;
    }
    else  
    {
        cout << ceil(p * ans) << endl;
    }
}
signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr),cout.tie(nullptr);
    int t = 1;
    /*  int t;
     cin >> t; */
    while(t -- ) solve();
    return 0;
}